The present invention relates to a storage cell for surface mounting for use in various types of electronic devices and, more particularly, to a horizontal-type storage cell for surface mounting which is suitable for high-density mounting on a printed wiring board.
There are an electric double layer capacitor, a button battery and the like as storage cells for surface mounting. In an electric double layer capacitor, for example, as is apparent from an outline of its configuration shown in FIG. 7, a pair of electric double layer electrodes 41a, 41b are disposed to oppose to each other through an insulating separator 44 and housed in a twofold metal container. In this pair of electric double layer electrodes, polarizable electrodes 43a, 43b each of an activated carbon layer are formed on disk-like sheets (or foil) 42a, 42b each of valve metal. The disk-like sheet (or foil) 42a of valve metal is bonded to the inner surface of a top cover 46 of the metal container and the disk-like sheet (or foil) 42b of valve metal is bonded to the inner surface of a case 45 of the metal container.
The case 45 and the top cover 46 are bonded together in a hermetically sealed manner, with a ring packing 47 interposed in a marginal area of the two, and a nonaqueous electrolyte (not shown) is charged into the interior of the metal container so as to fill up the electric double layer electrodes 41a, 41b and the separator 44.
A coin-shaped electric double layer capacitor 50 configured as described above is mounted on a printed wiring board, 53, 58 as shown in FIGS. 8A and 8B. FIG. 8A shows the coin-shaped electric double layer capacitor 50 vertically mounted on a substrate 53. External lead terminals 51, 52 are connected to the outer surface portions of the case 45 and top cover 46, respectively, of the electric double layer capacitor 50, and the external lead terminals 51, 52 are inserted into holes of the printed wiring board 53 and these portions are soldered. Also, FIG. 8B shows the coin-shaped electric double layer capacitor 50 horizontally mounted on the substrate 58. External lead terminals 56, 57 are connected to the outer surface portions of the case 45 and top cover 46, respectively, of the electric double layer capacitor 50, and the external lead terminals 56, 57 are inserted into holes of the printed wiring board 58 and these portions are soldered.
In addition to such a mounting method as described above, there is a method by which external lead terminals 62, 63 are connected to the outer surfaces of the case 45 and top cover 46 of the electric double layer capacitor 50, and the respective leading end portions of the external lead terminals 62, 63 kept parallel to the land surfaces 64a, 64b of a printed wiring board 64 are soldered by the reflow process.
On the other hand, also in a button battery, electrodes each having a separator interposed between a positive pole and a negative pole are housed in a twofold metal container and the external structure of this button battery is similar to that of the above-described electric double layer capacitor 50.
However, when a storage cell, such as an electric double layer capacitor and a button battery of the above-described configuration, is amounted on a printed wiring board for high-density mounting, the mounting height is large in a vertical type and the mounting area is large in a horizontal type, thus posing problems.
In a printed wiring board for high-density mounting, parts are mounted on both the front and back surfaces thereof. Therefore, after parts have been mounted on the front surface, these parts are caused to undergo displacement when the back surface of the printed wiring board is mounted with parts, with the result that problems such as poor contact or falling off of the parts may sometimes arise.
For this reason, large parts such as a coin-shaped storage cell are subjected to the reflow process after they are fixed onto a printed wiring board by use of an adhesive, posing a problem that the process becomes complicated.
Furthermore, in a case where a plurality of storage cells for surface mounting are connected in series, conventionally, a plurality of storage cells for surface mounting are inserted in a stacked manner into a case having a shape of cylinder, polygonal cylinder or the like, and the storage cells are brought into contact with each other under pressure by use of an electrically conductive elastic member such as a spring plate. Therefore, problems such as poor conductivity arose when an upsized substrate was used for mounting parts thereon, or when an urging force of an electrically conductive elastic member such as a spring plate is insufficient.
In order to solve such problems, it was conceivable to caulk a case having a plurality of storage cells for surface mounting inserted in a stacked state. However, if pressure for caulking increases, excessive stresses are applied to the storage cells and an electrolyte may leak. Thus, in view of reliability, it was difficult to introduce this method.
The present invention was made to solve such conventional problems and has as its object to provide a storage cell for surface mounting which can reduce the mounting area and increase the reliability of soldering even when high-density mounting is performed on a printed wiring board.
According to a first aspect of the invention, there is provided a storage cell for surface mounting, which includes: a polar storage cell having a component composed of a pair of electrodes and an insulative separator interposed between the pair of electrodes, the component being housed between a case disposed on an anode side of the component and a top cover disposed on a cathode side of the component and being sealed with an insulator; an anode terminal which is connected to an outer surface of the case; and a cathode terminal which is connected to an outer surface of the top cover. In this storage cell for surface mounting, the anode terminal is provided with an external connection which is connected to a printed wiring board, the cathode terminal is provided with an external connection which is connected to the printed wiring board and a fixing portion for mounting (or a mounting-fixing portion) which is connected to the top cover, and a plated layer is formed on the external connections of the anode terminal and cathode terminal and on the mounting-fixing portion of the cathode terminal. Because in mounting the storage cell for surface mounting on a printed wiring board, the mounting-fixing portion of the cathode terminal is also connected to a dummy land portion provided in the printed wiring board at the same time with each external connection, it is possible to reduce defects such as displacement and a short circuit caused by displacement even when the reflow process is performed after the mounting of the storage cell for surface mounting, and it is also possible to increase the reliability of soldering because each external connection has a plated layer.
In this first aspect of the invention, it is preferred that the plated layers formed in the external connections of the anode terminal and cathode terminal and the mounting-fixing portion of the cathode terminal be provided on the side where the storage cell for mounting is connected to the printed wiring board or on both sides.
Further, in the first aspect of the invention, the mounting area for mounting the storage cell for surface mounting on the printed wiring board can be reduced by arranging the anode terminal and the cathode terminal so that the external connection formed by bending one end of the anode terminal and the external connection of the cathode terminal are position in parallel in the same direction.
Further, in the first aspect of the invention, by positioning the mounting-fixing portion in the center of the top cover, the storage cell for surface mounting can be positively fixed to the printed wiring board, and the displacement and falling off of the storage cell can be reduced also in the later solder reflow process.
Further, in the first aspect of the invention, when a hole is cut out in the center of the mounting-fixing portion, a solder fillet is formed in the hole when the storage cell for surface mounting is connected to the printed wiring board and the strength of a soldered portion is increased, with the result that the reliability of soldering of the external connections can be further increased.
Furthermore, in the first aspect of the invention, when the plated layer is a tin-plated layer, the external connections and mounting-fixing portion can be easily mounted on the printed wiring board and hence connection of high reliability can be realized.
According to a second aspect of the invention, there is provided a storage cell for surface mounting comprising a plurality of polar storage cells laminated in series through a connection member, wherein an end of an anode terminal and an end of a cathode terminal are connected respectively to an anode terminal portion and a cathode terminal portion which provide both ends of the laminated polar storage cells, and the other end of the anode terminal and the other end of the cathode terminal are disposed on a same plane. Therefore, it is possible to realize a storage cell for surface mounting which ensures miniaturization and improvement in the reliability of bonding with a simple configuration and which enables high-density mounting on a printed wiring board to be performed.
Further, in the second aspect of the invention, when the connection member has a concave longitudinal sectional shape, the cathode of the polar storage cell is bonded to an outer bottom surface of the connection member and the anode of the polar storage cell is bonded to at least part of an inner circumferential surface of the connection member, then miniaturization can be achieved with a simple configuration and the reliability of bonding to the printed wiring board can be improved.
Further, in the second aspect of the invention, when one of the anode terminal connected to the anode of the laminated polar storage cells and the cathode terminal connected to the cathode is formed to be roughly linear and the other is bent into a channel shape, the miniaturization of the storage cell for surface mounting can be achieved with a simple configuration and high-density surface mounting can be performed with a minimum area.
Furthermore, in the second aspect of the invention, when an opening is formed in an area of the anode terminal or cathode terminal bent into the channel shape, the area being in contact with an outer peripheral surface of the polar storage cell, it is possible to increase the adhesion between the storage cell and the anode terminal or cathode terminal, and it becomes possible to form a solder fillet when the storage cell for surface mounting is mounted on the printed wiring board. Therefore, the reliability of the mounting state can be improved and it becomes possible to easily check a solder fillet in a post-mounting inspection.
As described above, according to the present invention, there is provided a storage cell for surface mounting, which comprises: a polar storage cell having a component composed of a pair of electrodes and an insulative separator interposed between the pair of electrodes, the component being housed between a case disposed on an anode side of the component and a top cover disposed on a cathode side of the component and being sealed with an insulator; an anode terminal which is connected to an outer surface of the above-described case; and a cathode terminal which is connected to an outer surface of the above-described top cover. In this storage cell for surface mounting, the anode terminal is provided with an external connection which is connected to a printed wiring board, the cathode terminal is provided with an external connection which is connected to the printed wiring board and a mounting-fixing portion which is connected to the top cover, and a plated layer is formed on the external connections of the anode terminal and cathode terminal and on the mounting-fixing portion of the cathode terminal. With this configuration, in mounting the storage cell for surface mounting on a printed wiring board, the fixing portion for mounting the cathode electrode can be connected to a dummy land portion provided in the printed wiring board, therefore, it is possible to reduce defects such as displacement and a short circuit caused by displacement even in the mounting reflow process after the storage cell for surface mounting has been mounted, and it is also possible to increase the reliability of soldering because each connection terminal has a plated layer. Thus the above advantages are obtained.
Furthermore, there is provided a storage cell for surface mounting, which comprises a plurality of polar storage cells laminated in series through a connection member, wherein an end of an anode terminal and an end of a cathode terminal are connected respectively to an anode and a cathode which provide both ends of the laminated polar storage cells, and the other end of the anode terminal and the other end of the cathode terminal are disposed on a same plane. Therefore, it is possible to realize a storage cell for surface mounting which ensures miniaturization and improvement in the reliability of bonding with a simple configuration without the need to use a dedicated case or the like, and which enables high-density mounting on a printed wiring board to be performed.